I’ve had a cracking return from mine, I’m on the 22p tariff and getting £850 a year in cash ,
4kw Array and directly south !
Have a look here. I used the site and the returns they projected were quite accurate if not a little pessimistic!
http://www.energysavingtrust.org.uk/renewable-energy/electricity/solar-panels
And:-
http://www.pvfitcalculator.energysavingtrust.org.uk/